HR Ultra slug for sure.
No.
A slug gn will cost you anywhere between $150-$400
ammunition means "to be fired from a gun" so slug ammunition means they use it as a bullet ,or with one ,or maybe they have a bullet as a shape of a slug
A single, non-rifled projectile shot out of a rifled bore shotgun (specifically a slug gun).
Gun shop, gun show, want ads
Federal law says you must be 18 to buy a long gun
No
Slug barrels were not made for auto 5's until 1962. These newer barrels will work, but need to be fitted. You may find a slug barrel for a 16ga on gunbroker.com either Belgian or Japanese, but you will need a qualified gunsmith to fit it to your gun.
currently all they offer is a 12 ga bolt gun
They don't make one for that gun.
Depending on where Hamilton is the answer could be yes or no.